If you need your 2018 AGI you can get a copy of your 2018 tax return, from TurboTax it will have your AGI. Follow these steps to get a copy of your prior-year tax return.
Sign in to TurboTax making sure you're using the same TurboTax account (with the same username) as in prior years.
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Select Documents from the navigation when it appears.
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Use the drop-down menu at the top of the screen to choose the tax year you want and then select Download PDF.
This link How do I access a prior year return? has additional information that you may find useful